U.S. Pat. No. 7,363,910 discloses an ignition device which includes a magnet wheel which rotates with the crankshaft and a stationary yoke having coils which is assigned to the magnet wheel. The magnet wheel carries two permanent magnets which are located diametrically opposite each other and which close the magnetic circuit of the yoke twice over the course of one rotation. A charging coil for charging the ignition capacitor is wound around one arm of the U-shaped yoke, while the ignition coil made up of a primary coil and a secondary coil is wound around the other arm. The arrangement of two magnets enables a strong, long-burning ignition spark which ensures reliable ignition of the mixture as well as a sufficient supply of energy for control units, actuators or sensors.
In unfavorable operating states, no ignition occurs over multiple revolutions of the combustion engine (for example, because of ignition suppression in order to limit the maximum rotational speed), so that, because of the scavenging principal of two stroke engines, the combustion chamber is also filled with mixture at the bottom dead center of the piston. In the case of atmospheric pressure in the combustion chamber, much lower voltages at the spark plug are sufficient to trigger an ignition spark than in the case of a mixture that is compressed, that is to say under positive pressure, in the combustion chamber. On account of the construction type of the magnet wheel and the ignition device, a voltage is induced in the coils by the two permanent magnets in the region of the bottom dead center, the induced voltage leading to a high voltage of 2 kV to 3 kV in the secondary coil. This can lead to an ignition spark at the spark plug at the atmospheric pressure that prevails in the combustion chamber in the region of the bottom dead center. If the combustion chamber is filled with combustible mixture because of an absence of combustion, this can lead to ignition of the mixture in the region of the bottom dead center of the piston. This leads to uncontrolled combustion and thus to irregular running of the engine.